Hydrostatic variable unit with a servo system and a valve unit controlling the servo system

Abstract

The invention relates to a hydrostatic variable unit with a servo system bringing about the control of the hydrostatic unit and with a valve unit controlling the servo system, the valve unit comprising two magnetically actuated proportional pressure-reducing valves which respectively act upon one of the sides of a servo system, which sides operate counter to each other, and having a safety function which, in the event of an incident, transfers the servo system into a safety position. The safety function is realized by at least one of the proportional pressure-reducing valves being designed at the same time as a pilot valve for activating and deactivating the second proportional pressure-reducing valve.

1 . Hydrostatic variable unit with a servo system bringing about the adjustment of the hydrostatic unit and with a valve unit controlling the servo system,
 the valve unit having a safety function which, in the event of an incident, transfers the servo system into a safety position,   the valve unit comprising two magnetically actuated proportional pressure-reducing valves,   the proportional pressure-reducing valves respectively acting upon one of the sides of a servo system, which sides operate counter to each other, and   the safety function being realized by at least one of the proportional pressure-reducing valves being designed at the same time as a pilot valve for activating and deactivating the second proportional pressure-reducing valve.   
   
   
       2 . Hydrostatic variable unit according to  claim 1 , in which the proportional pressure-reducing valve operating as the pilot valve is assigned a control piston which, as a function of its position, activates or deactivates the servo side assigned to the second proportional pressure-reducing valve. 
   
   
       3 . Hydrostatic variable unit according to  claim 1 , in which the proportional pressure-reducing valves are mutually designed in each case as a pilot valve for activating and deactivating the respectively other proportional pressure-reducing valve. 
   
   
       4 . Hydrostatic variable unit according to  claim 3 , in which a single control piston is provided for both proportional pressure-reducing valves. 
   
   
       5 . Hydrostatic variable unit according to  claim 4 , in which the control piston has a spring-centered neutral position. 
   
   
       6 . Hydrostatic variable unit according to  claim 4 , in which the spring centering of the control piston is realized by two identical centering devices on both sides of the control piston, the centering devices each having a rod guide with a spring pre-stressed thereon and with a disc which is displaceable in one direction and has a stop in the opposite direction. 
   
   
       7 . Hydrostatic variable unit according to  claim 4 , in which the control piston is arranged between opposite flanges of solenoids in such a manner that the flanges seal the control-piston bore. 
   
   
       8 . Hydrostatic variable unit according to  claim 1 , in which the deactivation of the proportional pressure-reducing valve comprises the interruption of the control lines between the proportional pressure-reducing valve and its assigned servo side. 
   
   
       9 . Hydrostatic variable unit according to  claim 8 , the assigned servo side being relieved of load towards the tank. 
   
   
       10 . Hydrostatic variable unit according to  claim 8 , both servo sides being relieved of load simultaneously towards the tank. 
   
   
       11 . Hydrostatic variable unit according to  claim 8 , both servo sides being connected to each other with the pressure being equalized. 
   
   
       12 . Hydrostatic variable unit according to  claim 11 , both servo sides being relieved of load at the same time towards the tank. 
   
   
       13 . Hydrostatic variable unit according  claim 1 , in which the deactivation comprises the interruption of the control lines for supplying pressure for the second proportional pressure-reducing valve. 
   
   
       14 . Hydrostatic variable unit according to  claim 13 , the control lines for supplying pressure for the second proportional pressure-reducing valve being relieved of load towards the tank. 
   
   
       15 . Hydrostatic variable unit according to  claim 13 , at least one servo side additionally being relieved of load towards the tank. 
   
   
       16 . Hydrostatic variable unit according to  claim 15 , in which both servo sides are bypassed. 
   
   
       17 . Hydrostatic variable unit according to  claim 10 , in which different orificing with a different delay of the tank-discharge operation is provided in the tank-discharge operations of the servo sides.